Compressor for a Refrigeration Device

ABSTRACT

A compressor for a refrigeration device comprising a compartment, a piston which can be displaced inside the compartment, and valves which are arranged between the compartment and a suction connection or a pressure connection. The movable parts of the valves are provided with a coating that is harder than the movable parts.

The present invention relates to a compressor which can be used in a refrigeration device for compressing refrigerant. Such a compressor generally comprises a chamber, a piston which can be moved in the chamber and valves arranged between the chamber and a suction connection or a pressure connection, which define the direction of flow through the compressor from the suction connection to the pressure connection.

Such compressors should have lifetimes of up to 15 years. This means that over this entire time the valves must remain sufficiently sealed to prevent any appreciable return flow of refrigerant from the pressure connection into the chamber or from the chamber to the suction connection of the compressor.

It is the object of the invention to provide a compressor whose valves have a particularly long lifetime.

This object is achieved by applying a coating to the movable parts of the valves which is harder than said movable parts and protects from abrasion and deformation when acting upon other parts of the valve, in particular during their closing movement.

A ceramic coating can be considered in particular as a hard coating.

Such a ceramic coating can be formed, for example, by applying material to the movable parts, for example, by applying a suspension of ceramic particles and subsequent sintering.

A particularly close bond between the movable part and the ceramic layer formed thereon is obtained if the ceramic layer is formed by surface conversion of the material of the movable parts.

Oxides, nitrides, carbides or a mixture of several of these substances can be considered in particular as the material of the ceramic coating.

Preferably a spring steel is used as material for the movable parts.

The invention can be applied particularly advantageously in a compressor comprising a linear drive unit acting directly on the piston since such compressors, as are known, for example, from U.S. Pat. No. 6,641,377 B2, have a relatively small piston stroke compared with rotary-driven compressors and must therefore operate at a high movement frequency and accordingly frequent switching of the valves in order to achieve a required throughput.

Furthermore, the invention can be advantageously applied when the piston is mounted in an oil-free manner in the chamber. Whereas in the case of oil-mounted pistons a thin film of oil usually covers the entire interior of the chamber, including the valves, which promotes the removal of heat from the movable parts of the valves, the removal of heat from the movable parts in oil-free operation is usually significantly inferior and consequently, the thermal loading and therefore also the tendency of these movable parts to wear is high.

An exemplary embodiment of the invention is described in detail hereinafter with reference to the appended figures: in the figures:

FIG. 1 is a compressor according to the invention, partly in a schematic side view, partly in section; and

FIG. 2 is a plan view of a membrane spring of the compressor from FIG. 1.

A drive unit 1 forms the lower region of the linear compressor shown in the figure. This comprises a permanent-magnet vibrating body 2, the longitudinal ends whereof form respectively opposite magnet poles. The vibrating body 2 extends through two opposing openings 3 of a chamber 4 which are provided to receive a pair of electromagnets 8. The diametrically opposed electromagnets 8 on both sides of the vibrating body 2 can be energised with an alternating current of controlled frequency to generate alternating magnetic fields having like poles respectively opposite to one another. The electromagnets 8 have an iron core 9 having an E-shaped cross-section with three parallel legs 11, 12 connected at one end. A winding 10 surrounds the middle legs 11 of each iron core. The tip of the middle leg 11 on the one hand and those of the two outer legs 12 on the other hand each form unlike poles of each electromagnet 8.

Depending on the direction of the exciting current of the electromagnets 8, the poles at the tips of the leg 12 in each case alternately attract one of the poles of the vibrating body 2 and repel the other and thereby deflect the vibrating body 2 alternately in opposite directions.

The longitudinal ends of the vibrating body 2 are each fastened to a membrane spring 5 which is held at a distance from the walls of the chamber 4 by webs 6. As shown in the plan view in FIG. 2, four approximately z-shaped arms 7 are stamped out from each membrane spring 5 and are held together in one piece at the height of the end of the vibrating body 2 held by the relevant membrane spring 5. In the plan view, each arm 7 occupies a 90° sector emanating from the longitudinal axis of the vibrating body 2 and each arm 7 is formed as a mirror image to the two neighbouring arms 7. Two of these arms 7 can be seen in each case in FIG. 1 which shows the vibrating body 2 deflected slightly upwards from its rest position. The mirror-symmetrical arrangement compensates for a torque that one of the arms 7 possibly exerts thereon in the course of the movement of the vibrating body 2 as a result of the equal and opposite torque of the neighbouring arm.

A compressor chamber is connected to the chamber 4 of the electromagnet via a bend 21 which is fastened to the webs 6 of the upper side of the chamber 4 via the ends of the arms 7 of the upper membrane spring 5 facing away from the vibrating body. A piston rod 22 connects a piston 23 which can move to and fro in the compressor chamber 20 to the vibrating body 2 so that both form a system capable of vibrating, its eigenfrequency being substantially determined by the mass of the vibrating body 2, the piston 23 and the piston rod 22 as well as the spring constant of the membrane springs 5.

A suction connection 24 and a pressure connection 25 each open via an inlet valve 26 or an outlet valve 27 into the compressor chamber 20. The valves 26, 27 are shown as plate valves here as an example, each having a spring leaf 28 which is soldered at one end to the wall of the compressor chamber 20, or fastened in another suitable manner, and which bears a sealing body 29 in its movable section which is in contact with a hollow-conical valve seat 30 formed in the wall of the compressor chamber 20 in the configuration shown in FIG. 1. The spring leaf 28 is formed of spring steel in each case. The sealing body 29 can be formed completely as a ceramic layer secured to the spring leaf 28; it can also consist of spring steel in the core and merely be provided with an outer coating which is too thin to be shown in the figure. In the latter case, the sealing body 29 is preferably formed by embossing in one piece from the material of the spring leaf 28.

Whereas the spring leaf 28 of the inlet valve 26 is arranged directly in the compressor chamber 20 and can withdraw into its interior, when the piston 23 moves downwards and fluid is sucked into the compressor chamber 20 from the suction connection 24, the outlet valve 27 is located in a separate chamber 31 inside the wall of the compressor chamber into which it can withdraw to allow fluid displaced by the upwardly moving piston 23 to flow to the pressure connection. A passage 32 which supplies compressed fluid to a cavity 33 which surrounds the compressor chamber 20 in a ring shape goes out from the chamber 31. The cavity 33 communicates with the interior of the compressor chamber 20 via a plurality of radial holes 24 through which some of the fluid displaced by the piston 23 can flow back into the compressor chamber 20. This forms a sliding film between the inner wall of the compressor chamber 20 and the circumferential face of the piston 23 which allows this to slide largely free from friction and allows oil lubrication of the piston 23 to be dispensed with.

The wear-reducing hard surface layer can be restricted to those surface areas of the sealing body 29 which actually come in contact with the valve seat 30; however, it can also extend over the entire sealing body or, particularly when this is formed in one piece from the spring leaf 28, over the entire surface of the spring leaf 28 or at least its side facing the valve seat 30. Said coating can be produced by converting a surface layer of the sealing body in a reactive, e.g. oxygen-containing atmosphere or in a plasma containing oxygen, nitrogen and/or carbon to form an oxide, nitride or carbide, in which case the surface layer to be converted can be part of the spring steel of the sealing body 29 itself or it can be material applied beforehand for the purposes of conversion or the desired ceramic material such as aluminium oxide or zirconium oxides, e.g. in the form of a suspension or a gel can be applied or sprayed directly onto the relevant surface and then sintered thereon. 

1-9. (canceled)
 10. A compressor for a refrigeration device comprising: a chamber; a piston which can move in the chamber; and valves arranged between the chamber and a suction connection or a pressure connection, wherein a hard coating is applied to movable parts of the valves, the hard coating being harder than said movable parts.
 11. The compressor according to claim 10, wherein the hard coating is a ceramic coating.
 12. The compressor according to claim 11, wherein the ceramic coating is formed by applying material to the movable parts.
 13. The compressor according to claim 11, wherein the ceramic coating is formed by surface conversion of the material of the movable parts.
 14. The compressor according to claim 11, wherein the ceramic coating is an oxide, a nitride, a carbide or a mixture thereof.
 15. The compressor according to claim 10, wherein the material of the movable parts is a spring steel.
 16. The compressor according to claim 10, wherein the compressor comprises a linear drive unit acting directly on the piston.
 17. The compressor according to claim 10, wherein the piston is mounted in an oil-free manner in the chamber.
 18. The compressor according to claim 17, wherein the piston is mounted by means of compressed fluid branched off from the pressure connection. 